Goal:
I want to combine information from two tables (entityA & entityB) with different Properties to one unionDto. I am trying to implement this with a union operation to filter different entities in the Database at the same time.
But the structure I am using requires Versions which need to be filtered before the union query.
Some Additional Information:
So what I am trying to do in the last query is: First I project information from table "entityA" and "entityB" to a universal "anonymous" type (with union). Then I am trying to apply pagination and then I am trying to "project" the new anonymous result to a UnionDto. So this would result in one UnionDto which has "information from 2 different tables".
I have created an example of my problem with two entities which have Versions:
Entities:
class entityA {
public List<VersionA> Versions;
public Guid CreatedBy;
}
class entityB {
public List<VersionB> Versions;
public Guid CreatedBy;
}
class VersionA {
public string TitleA;
public Instant EffectiveTo;
}
class VersionB {
public string TitleB;
public Instant EffectiveTo;
}
class UnionDto{
public string Title;
public Guid Creator;
}
I am setting up the query like this:
var queryA = databaseContext.Set<entityA>()
.Select(entity => new
{
Versions = entity.Versions
.Where(version => version.EffectiveTo > now) /* Filtering newest entity Version */
.Select(versionDetail => new /* Selecting only the Title of this Version */
{
Title = versionDetail.TitleA
})
.ToList(),
Creator = entity.CreatedBy,
});
var queryB = databaseContext.Set<entityB>()
.Select(entity => new
{
Versions = entity.Versions
.Where(version => version.EffectiveTo > now)
.Select(versionDetail => new
{
Title = versionDetail.TitleB
})
.ToList(),
Creator = entity.CreatedBy,
});
Executing the query:
var unionDto = await queryA
.Union(queryB)
.Skip(0)
.Take(20)
.Select(x => new UnionDto
{
Title= x.Versions.FirstOrDefault() == null ? null :
x.Versions.FirstOrDefault().Title,
Creator= x.Creator,
})
.ToListAsync();
It seems like that i am not able to use sub selects inside a union query and I am getting the following error:
Set operations: support when placed after client evaluation in
projection #16243
I dont know, what I have to do to get around this issue, since I dont really want to go throught all of my entities seperatly with seperate Database queries.
Currently using Ef core Version: 5.0.100-preview
Now this is just an example. This would be required for at least 10 entities, which would result in high Database traffic if done for each entity seperatly.
Any ideas?
If you need only title of first version from each recordset, your query can be simplified and EF Core can translate this query.
var queryA =
from entity in databaseContext.Set<entityA>()
from version in entity.Versions
where version.EffectiveTo > now
select new
{
Title = version.Title,
Creator = entity.CreatedBy
}
var queryB =
from entity in databaseContext.Set<entityB>()
from version in entity.Versions
where version.EffectiveTo > now
select new
{
Title = version.Title,
Creator = entity.CreatedBy
}
var versions = queryA.Union(queryB);
var unionDto = await versions
.Skip(0)
.Take(20)
.Select(x => new UnionDto
{
Title = x.Title,
Creator = x.Creator,
})
.ToListAsync();
Having the following example:
var myIds = db.Table1.Where(x=>x.Prop2 == myFilter).Select(x=>x.Id).ToList();
var results = db.Table2.Where(x=> myIds.Contains(x.T1)).ToList();
This part is straight forward.
However, now I am facing a "slight" change where my "filter list" has 2 properties instead of only one:
// NOTE: for stackoverflow simplification I use a basic query to
// get my "myCombinationObject".
// In reality this is a much more complex case,
// but the end result is a LIST of objects with two properties.
var myCombinationObject = db.Table3.Where(x=>x.Prop3 == myFilter)
.Select(x=> new {
Id1 = x.T1,
Id2 = x.T2
}).ToList();
var myCombinationObjectId1s = myCombinationObject.Select(x=>xId1).ToList();
var myCombinationObjectId2s = myCombinationObject.Select(x=>xId2).ToList();
// step#1 - DB SQL part
var resultsRaw = db.Tables.Where( x=>
myCombinationObjectId1s.Contains(x.Prop1)
|| myCombinationObjectId2s.Contains(x.Prop2))
.ToList();
// step#2 - Now in memory side - where I make the final combination filter.
var resultsFiltered = resultsRaw.Where( x=>
myCombinationObject.Contains(
new {Id1 = x.Prop1, Id2 = x.Prop2 }
).ToList();
My question: is it even possible to merge the step#2 in the step#1 (query in linq to entities) ?
I've managed once to do what you want, however it is pretty hard and requires changing entity model a bit. You need an entity to map type
new {Id1 = x.Prop1, Id2 = x.Prop2 }
So you need enity having 2 properties - Id1 and Id2. If you have one - great, if not then add such entity to your model:
public class CombinationObjectTable
{
public virtual Guid Id1 { get; set; }
public virtual Guid Id2 { get; set; }
}
Add it to your model:
public DbSet<CombinationObjectTable> CombinationObjectTable { get; set; }
Create new migration and apply it database (database will have now additional table CombinationObjectTable). After that you start to build a query:
DbSet<CombinationObjectTable> combinationObjectTable = context.Set<CombinationObjectTable>();
StringBuilder wholeQuery = new StringBuilder("DELETE * FROM CombinationObjectTable");
foreach(var obj in myCombinationObject)
{
wholeQuery.Append(string.Format("INSERT INTO CombinationObjectTable(Id1, Id2) VALUES('{0}', '{1}')", obj.Id1, obj.Id2);
}
wholeQuery.Append(
db.Tables
.Where( x=>
myCombinationObjectId1s.Contains(x.Prop1)
|| myCombinationObjectId2s.Contains(x.Prop2))
.Where( x=>
combinationObjectTable.Any(ct => ct.Id1 == x.Id1 && ct.Id2 == x.Id2)
).ToString();
);
var filteredResults = context.Tables.ExecuteQuery(wholeQuery.ToString());
Thanks to this your main query stays written in linq. If you do not want to add new table to your db this is as well achievable. Add new class CombinationObjectTable to model, generate new migration to add it and afterwards remove code creating that table from migration code. After that apply migration. This way the db schema won't be changed but EF will think that there is CombinationObjectTable in database. Instead of it you will need to create a temporary table to hold data:
StringBuilder wholeQuery = new StringBuilder("CREATE TABLE #TempCombinationObjectTable(Id1 uniqueidentifies, Id2 uniqueidentifier);");
And when you invoke ToString method on your linq query change CombinationObjectTable to #TempCombinationObjectTable:
...
.ToString()
.Replace("CombinationObjectTable", "#TempCombinationObjectTable")
Other thing worth considering would be using query parameters to pass values in INSERT statements instead of just including them in query yourself - this is of course achievable with EF as well. This solution is not fully ready to apply, rather some hint in which direction you may go for the solution.
Can you do something like this:
var result=
db.Tables
.Where(t=>
db.Table3
.Where(x=>x.Prop3 == myFilter)
.Any(a=>a.T1==t.Prop1 || a.T2==t.Prop2)
).ToList();
If you simply want to avoid the intermediate result (and also creating a second intermediary list) you can do the following
var resultsFiltered = db.Tables.Where( x=>
myCombinationObjectId1s.Contains(x.Prop1)
|| myCombinationObjectId2s.Contains(x.Prop2))
.AsEnumerable() // everything past that is done in memory but isn't materialized immediately, keeping the streamed logic of linq
.Where( x=>
myCombinationObject
.Contains(new {Id1 = x.Prop1, Id2 = x.Prop2 })
.ToList();
given a list of ids, I can query all relevant rows by:
context.Table.Where(q => listOfIds.Contains(q.Id));
But how do you achieve the same functionality when the Table has a composite key?
This is a nasty problem for which I don't know any elegant solution.
Suppose you have these key combinations, and you only want to select the marked ones (*).
Id1 Id2
--- ---
1 2 *
1 3
1 6
2 2 *
2 3 *
... (many more)
How to do this is a way that Entity Framework is happy? Let's look at some possible solutions and see if they're any good.
Solution 1: Join (or Contains) with pairs
The best solution would be to create a list of the pairs you want, for instance Tuples, (List<Tuple<int,int>>) and join the database data with this list:
from entity in db.Table // db is a DbContext
join pair in Tuples on new { entity.Id1, entity.Id2 }
equals new { Id1 = pair.Item1, Id2 = pair.Item2 }
select entity
In LINQ to objects this would be perfect, but, too bad, EF will throw an exception like
Unable to create a constant value of type 'System.Tuple`2 (...) Only primitive types or enumeration types are supported in this context.
which is a rather clumsy way to tell you that it can't translate this statement into SQL, because Tuples is not a list of primitive values (like int or string). For the same reason a similar statement using Contains (or any other LINQ statement) would fail.
Solution 2: In-memory
Of course we could turn the problem into simple LINQ to objects like so:
from entity in db.Table.AsEnumerable() // fetch db.Table into memory first
join pair Tuples on new { entity.Id1, entity.Id2 }
equals new { Id1 = pair.Item1, Id2 = pair.Item2 }
select entity
Needless to say that this is not a good solution. db.Table could contain millions of records.
Solution 3: Two Contains statements (incorrect)
So let's offer EF two lists of primitive values, [1,2] for Id1 and [2,3] for Id2. We don't want to use join, so let's use Contains:
from entity in db.Table
where ids1.Contains(entity.Id1) && ids2.Contains(entity.Id2)
select entity
But now the results also contains entity {1,3}! Well, of course, this entity perfectly matches the two predicates. But let's keep in mind that we're getting closer. In stead of pulling millions of entities into memory, we now only get four of them.
Solution 4: One Contains with computed values
Solution 3 failed because the two separate Contains statements don't only filter the combinations of their values. What if we create a list of combinations first and try to match these combinations? We know from solution 1 that this list should contain primitive values. For instance:
var computed = ids1.Zip(ids2, (i1,i2) => i1 * i2); // [2,6]
and the LINQ statement:
from entity in db.Table
where computed.Contains(entity.Id1 * entity.Id2)
select entity
There are some problems with this approach. First, you'll see that this also returns entity {1,6}. The combination function (a*b) does not produce values that uniquely identify a pair in the database. Now we could create a list of strings like ["Id1=1,Id2=2","Id1=2,Id2=3]" and do
from entity in db.Table
where computed.Contains("Id1=" + entity.Id1 + "," + "Id2=" + entity.Id2)
select entity
(This would work in EF6, not in earlier versions).
This is getting pretty messy. But a more important problem is that this solution is not sargable, which means: it bypasses any database indexes on Id1 and Id2 that could have been used otherwise. This will perform very very poorly.
Solution 5: Best of 2 and 3
So the most viable solution I can think of is a combination of Contains and a join in memory: First do the contains statement as in solution 3. Remember, it got us very close to what we wanted. Then refine the query result by joining the result as an in-memory list:
var rawSelection = from entity in db.Table
where ids1.Contains(entity.Id1) && ids2.Contains(entity.Id2)
select entity;
var refined = from entity in rawSelection.AsEnumerable()
join pair in Tuples on new { entity.Id1, entity.Id2 }
equals new { Id1 = pair.Item1, Id2 = pair.Item2 }
select entity;
It's not elegant, messy all the same maybe, but so far it's the only scalable1 solution to this problem I found, and applied in my own code.
Solution 6: Build a query with OR clauses
Using a Predicate builder like Linqkit or alternatives, you can build a query that contains an OR clause for each element in the list of combinations. This could be a viable option for really short lists. With a couple of hundreds of elements, the query will start performing very poorly. So I don't consider this a good solution unless you can be 100% sure that there will always be a small number of elements. One elaboration of this option can be found here.
Solution 7: Unions
There's also a solution using UNIONs that I posted later here.
1As far as the Contains statement is scalable: Scalable Contains method for LINQ against a SQL backend
Solution for Entity Framework Core with SQL Server
🎉 NEW! QueryableValues EF6 Edition has arrived!
The following solution makes use of QueryableValues. This is a library that I wrote to primarily solve the problem of query plan cache pollution in SQL Server caused by queries that compose local values using the Contains LINQ method. It also allows you to compose values of complex types in your queries in a performant way, which will achieve what's being asked in this question.
First you will need to install and set up the library, after doing that you can use any of the following patterns that will allow you to query your entities using a composite key:
// Required to make the AsQueryableValues method available on the DbContext.
using BlazarTech.QueryableValues;
// Local data that will be used to query by the composite key
// of the fictitious OrderProduct table.
var values = new[]
{
new { OrderId = 1, ProductId = 10 },
new { OrderId = 2, ProductId = 20 },
new { OrderId = 3, ProductId = 30 }
};
// Optional helper variable (needed by the second example due to CS0854)
var queryableValues = dbContext.AsQueryableValues(values);
// Example 1 - Using a Join (preferred).
var example1Results = dbContext
.OrderProduct
.Join(
queryableValues,
e => new { e.OrderId, e.ProductId },
v => new { v.OrderId, v.ProductId },
(e, v) => e
)
.ToList();
// Example 2 - Using Any (similar behavior as Contains).
var example2Results = dbContext
.OrderProduct
.Where(e => queryableValues
.Where(v =>
v.OrderId == e.OrderId &&
v.ProductId == e.ProductId
)
.Any()
)
.ToList();
Useful Links
Nuget Package
GitHub Repository
Benchmarks
QueryableValues is distributed under the MIT license.
You can use Union for each composite primary key:
var compositeKeys = new List<CK>
{
new CK { id1 = 1, id2 = 2 },
new CK { id1 = 1, id2 = 3 },
new CK { id1 = 2, id2 = 4 }
};
IQuerable<CK> query = null;
foreach(var ck in compositeKeys)
{
var temp = context.Table.Where(x => x.id1 == ck.id1 && x.id2 == ck.id2);
query = query == null ? temp : query.Union(temp);
}
var result = query.ToList();
You can create a collection of strings with both keys like this (I am assuming that your keys are int type):
var id1id2Strings = listOfIds.Select(p => p.Id1+ "-" + p.Id2);
Then you can just use "Contains" on your db:
using (dbEntities context = new dbEntities())
{
var rec = await context.Table1.Where(entity => id1id2Strings .Contains(entity.Id1+ "-" + entity.Id2));
return rec.ToList();
}
You need a set of objects representing the keys you want to query.
class Key
{
int Id1 {get;set;}
int Id2 {get;set;}
If you have two lists and you simply check that each value appears in their respective list then you are getting the cartesian product of the lists - which is likely not what you want. Instead you need to query the specific combinations required
List<Key> keys = // get keys;
context.Table.Where(q => keys.Any(k => k.Id1 == q.Id1 && k.Id2 == q.Id2));
I'm not completely sure that this is valid use of Entity Framework; you may have issues with sending the Key type to the database. If that happens then you can be creative:
var composites = keys.Select(k => p1 * k.Id1 + p2 * k.Id2).ToList();
context.Table.Where(q => composites.Contains(p1 * q.Id1 + p2 * q.Id2));
You can create an isomorphic function (prime numbers are good for this), something like a hashcode, which you can use to compare the pair of values. As long as the multiplicative factors are co-prime this pattern will be isomorphic (one-to-one) - i.e. the result of p1*Id1 + p2*Id2 will uniquely identify the values of Id1 and Id2 as long as the prime numbers are correctly chosen.
But then you end up in a situation where you're implementing complex concepts and someone is going to have to support this. Probably better to write a stored procedure which takes the valid key objects.
Ran into this issue as well and needed a solution that both did not perform a table scan and also provided exact matches.
This can be achieved by combining Solution 3 and Solution 4 from Gert Arnold's Answer
var firstIds = results.Select(r => r.FirstId);
var secondIds = results.Select(r => r.SecondId);
var compositeIds = results.Select(r => $"{r.FirstId}:{r.SecondId}");
var query = from e in dbContext.Table
//first check the indexes to avoid a table scan
where firstIds.Contains(e.FirstId) && secondIds.Contains(e.SecondId))
//then compare the compositeId for an exact match
//ToString() must be called unless using EF Core 5+
where compositeIds.Contains(e.FirstId.ToString() + ":" + e.SecondId.ToString()))
select e;
var entities = await query.ToListAsync();
For EF Core I use a slightly modified version of the bucketized IN method by EricEJ to map composite keys as tuples. It performs pretty well for small sets of data.
Sample usage
List<(int Id, int Id2)> listOfIds = ...
context.Table.In(listOfIds, q => q.Id, q => q.Id2);
Implementation
public static IQueryable<TQuery> In<TKey1, TKey2, TQuery>(
this IQueryable<TQuery> queryable,
IEnumerable<(TKey1, TKey2)> values,
Expression<Func<TQuery, TKey1>> key1Selector,
Expression<Func<TQuery, TKey2>> key2Selector)
{
if (values is null)
{
throw new ArgumentNullException(nameof(values));
}
if (key1Selector is null)
{
throw new ArgumentNullException(nameof(key1Selector));
}
if (key2Selector is null)
{
throw new ArgumentNullException(nameof(key2Selector));
}
if (!values.Any())
{
return queryable.Take(0);
}
var distinctValues = Bucketize(values);
if (distinctValues.Length > 1024)
{
throw new ArgumentException("Too many parameters for SQL Server, reduce the number of parameters", nameof(values));
}
var predicates = distinctValues
.Select(v =>
{
// Create an expression that captures the variable so EF can turn this into a parameterized SQL query
Expression<Func<TKey1>> value1AsExpression = () => v.Item1;
Expression<Func<TKey2>> value2AsExpression = () => v.Item2;
var firstEqual = Expression.Equal(key1Selector.Body, value1AsExpression.Body);
var visitor = new ReplaceParameterVisitor(key2Selector.Parameters[0], key1Selector.Parameters[0]);
var secondEqual = Expression.Equal(visitor.Visit(key2Selector.Body), value2AsExpression.Body);
return Expression.AndAlso(firstEqual, secondEqual);
})
.ToList();
while (predicates.Count > 1)
{
predicates = PairWise(predicates).Select(p => Expression.OrElse(p.Item1, p.Item2)).ToList();
}
var body = predicates.Single();
var clause = Expression.Lambda<Func<TQuery, bool>>(body, key1Selector.Parameters[0]);
return queryable.Where(clause);
}
class ReplaceParameterVisitor : ExpressionVisitor
{
private ParameterExpression _oldParameter;
private ParameterExpression _newParameter;
public ReplaceParameterVisitor(ParameterExpression oldParameter, ParameterExpression newParameter)
{
_oldParameter = oldParameter;
_newParameter = newParameter;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (ReferenceEquals(node, _oldParameter))
return _newParameter;
return base.VisitParameter(node);
}
}
/// <summary>
/// Break a list of items tuples of pairs.
/// </summary>
private static IEnumerable<(T, T)> PairWise<T>(this IEnumerable<T> source)
{
var sourceEnumerator = source.GetEnumerator();
while (sourceEnumerator.MoveNext())
{
var a = sourceEnumerator.Current;
sourceEnumerator.MoveNext();
var b = sourceEnumerator.Current;
yield return (a, b);
}
}
private static TKey[] Bucketize<TKey>(IEnumerable<TKey> values)
{
var distinctValueList = values.Distinct().ToList();
// Calculate bucket size as 1,2,4,8,16,32,64,...
var bucket = 1;
while (distinctValueList.Count > bucket)
{
bucket *= 2;
}
// Fill all slots.
var lastValue = distinctValueList.Last();
for (var index = distinctValueList.Count; index < bucket; index++)
{
distinctValueList.Add(lastValue);
}
var distinctValues = distinctValueList.ToArray();
return distinctValues;
}
In the absence of a general solution, I think there are two things to consider:
Avoid multi-column primary keys (will make unit testing easier too).
But if you have to, chances are that one of them will reduce the
query result size to O(n) where n is the size of the ideal query
result. From here, its Solution 5 from Gerd Arnold above.
For example, the problem leading me to this question was querying order lines, where the key is order id + order line number + order type, and the source had the order type being implicit. That is, the order type was a constant, order ID would reduce the query set to order lines of relevant orders, and there would usually be 5 or less of these per order.
To rephrase: If you have a composite key, changes are that one of them have very few duplicates. Apply Solution 5 from above with that.
I tried this solution and it worked with me and the output query was perfect without any parameters
using LinqKit; // nuget
var customField_Ids = customFields?.Select(t => new CustomFieldKey { Id = t.Id, TicketId = t.TicketId }).ToList();
var uniqueIds1 = customField_Ids.Select(cf => cf.Id).Distinct().ToList();
var uniqueIds2 = customField_Ids.Select(cf => cf.TicketId).Distinct().ToList();
var predicate = PredicateBuilder.New<CustomFieldKey>(false); //LinqKit
var lambdas = new List<Expression<Func<CustomFieldKey, bool>>>();
foreach (var cfKey in customField_Ids)
{
var id = uniqueIds1.Where(uid => uid == cfKey.Id).Take(1).ToList();
var ticketId = uniqueIds2.Where(uid => uid == cfKey.TicketId).Take(1).ToList();
lambdas.Add(t => id.Contains(t.Id) && ticketId.Contains(t.TicketId));
}
predicate = AggregateExtensions.AggregateBalanced(lambdas.ToArray(), (expr1, expr2) =>
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<CustomFieldKey, bool>>
(Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
});
var modifiedCustomField_Ids = repository.GetTable<CustomFieldLocal>()
.Select(cf => new CustomFieldKey() { Id = cf.Id, TicketId = cf.TicketId }).Where(predicate).ToArray();
I ended up writing a helper for this problem that relies on System.Linq.Dynamic.Core;
Its a lot of code and don't have time to refactor at the moment but input / suggestions appreciated.
public static IQueryable<TEntity> WhereIsOneOf<TEntity, TSource>(this IQueryable<TEntity> dbSet,
IEnumerable<TSource> source,
Expression<Func<TEntity, TSource,bool>> predicate) where TEntity : class
{
var (where, pDict) = GetEntityPredicate(predicate, source);
return dbSet.Where(where, pDict);
(string WhereStr, IDictionary<string, object> paramDict) GetEntityPredicate(Expression<Func<TEntity, TSource, bool>> func, IEnumerable<TSource> source)
{
var firstP = func.Parameters[0];
var binaryExpressions = RecurseBinaryExpressions((BinaryExpression)func.Body);
var i = 0;
var paramDict = new Dictionary<string, object>();
var res = new List<string>();
foreach (var sourceItem in source)
{
var innerRes = new List<string>();
foreach (var bExp in binaryExpressions)
{
var emp = ToEMemberPredicate(firstP, bExp);
var val = emp.GetKeyValue(sourceItem);
var pName = $"#{i++}";
paramDict.Add(pName, val);
var str = $"{emp.EntityMemberName} {emp.SQLOperator} {pName}";
innerRes.Add(str);
}
res.Add( "(" + string.Join(" and ", innerRes) + ")");
}
var sRes = string.Join(" || ", res);
return (sRes, paramDict);
}
EMemberPredicate ToEMemberPredicate(ParameterExpression firstP, BinaryExpression bExp)
{
var lMember = (MemberExpression)bExp.Left;
var rMember = (MemberExpression)bExp.Right;
var entityMember = lMember.Expression == firstP ? lMember : rMember;
var keyMember = entityMember == lMember ? rMember : lMember;
return new EMemberPredicate(entityMember, keyMember, bExp.NodeType);
}
List<BinaryExpression> RecurseBinaryExpressions(BinaryExpression e, List<BinaryExpression> runningList = null)
{
if (runningList == null) runningList = new List<BinaryExpression>();
if (e.Left is BinaryExpression lbe)
{
var additions = RecurseBinaryExpressions(lbe);
runningList.AddRange(additions);
}
if (e.Right is BinaryExpression rbe)
{
var additions = RecurseBinaryExpressions(rbe);
runningList.AddRange(additions);
}
if (e.Left is MemberExpression && e.Right is MemberExpression)
{
runningList.Add(e);
}
return runningList;
}
}
Helper class:
public class EMemberPredicate
{
public readonly MemberExpression EntityMember;
public readonly MemberExpression KeyMember;
public readonly PropertyInfo KeyMemberPropInfo;
public readonly string EntityMemberName;
public readonly string SQLOperator;
public EMemberPredicate(MemberExpression entityMember, MemberExpression keyMember, ExpressionType eType)
{
EntityMember = entityMember;
KeyMember = keyMember;
KeyMemberPropInfo = (PropertyInfo)keyMember.Member;
EntityMemberName = entityMember.Member.Name;
SQLOperator = BinaryExpressionToMSSQLOperator(eType);
}
public object GetKeyValue(object o)
{
return KeyMemberPropInfo.GetValue(o, null);
}
private string BinaryExpressionToMSSQLOperator(ExpressionType eType)
{
switch (eType)
{
case ExpressionType.Equal:
return "==";
case ExpressionType.GreaterThan:
return ">";
case ExpressionType.GreaterThanOrEqual:
return ">=";
case ExpressionType.LessThan:
return "<";
case ExpressionType.LessThanOrEqual:
return "<=";
case ExpressionType.NotEqual:
return "<>";
default:
throw new ArgumentException($"{eType} is not a handled Expression Type.");
}
}
}
Use Like so:
// This can be a Tuple or whatever.. If Tuple, then y below would be .Item1, etc.
// This data structure is up to you but is what I use.
[FromBody] List<CustomerAddressPk> cKeys
var res = await dbCtx.CustomerAddress
.WhereIsOneOf(cKeys, (x, y) => y.CustomerId == x.CustomerId
&& x.AddressId == y.AddressId)
.ToListAsync();
Hope this helps others.
in Case of composite key you can use another idlist and add a condition for that in your code
context.Table.Where(q => listOfIds.Contains(q.Id) && listOfIds2.Contains(q.Id2));
or you can use one another trick create a list of your keys by adding them
listofid.add(id+id1+......)
context.Table.Where(q => listOfIds.Contains(q.Id+q.id1+.......));
I tried this on EF Core 5.0.3 with the Postgres provider.
context.Table
.Select(entity => new
{
Entity = entity,
CompositeKey = entity.Id1 + entity.Id2,
})
.Where(x => compositeKeys.Contains(x.CompositeKey))
.Select(x => x.Entity);
This produced SQL like:
SELECT *
FROM table AS t
WHERE t.Id1 + t.Id2 IN (#__compositeKeys_0)),
Caveats
this should only be used where the combination of Id1 and Id2 will always produce a unique result (e.g., they're both UUIDs)
this cannot use indexes, though you could save the composite key to the db with an index
What's the equivalent LINQ instruction for a Datatable of the following SQL query:
SELECT code_direction, count(TP) AS CN
FROM table1
WHERE cod_time = 'A011'
GROUP BY TP,code_direction;
and how to get the result into a new datatable?
I tried to convert it but I there're some errors. Someone could take a look on this:
var query = from t in table1.AsEnumerable()
group t by new { t.TP, t.code_direction }
into grp
select new
{
grp.Key.code_direction,
CN = grp.Count(t.TP)
};
foreach (var x in query)
{
Console.Write(x.code_direction);
Console.Write(x.CN);
}
As far as your first question goes. The LINQ equivalent of the SQL query is:
var query = from t in table1.AsEnumerable()
where t.cod_time == "A011"
group t by new { t.TP, t.code_direction }
into grp
select new
{
grp.Key.code_direction,
CN = grp.Count()
};
Note that you don't have to pass any argument to grp.Count(). (For the obvious reason that in SQL COUNT(TP) is the same as COUNT(*), i.e. just count the number of rows. The story would be different if you'd use COUNT(DISTINCT TP) or similar.)
As far as the second question goes, if your query just returned an IEnumerable<T> where T is DataRow (i.e. a query like table1.AsEnumerable().Where(r => r.cod_time == "A011")) then you could just the DataTableExtensions.CopyToDataTable extension method. As your query returns an anonymous type however, you will have to follow these instructions found on MSDN.
I Have been using LINQ to work on a JSON object returned from a remote sharepoint web service. I have posted this because most of the answers I found online were slightly different from what I needed.
a json list of daily activities is returned from a remote sharepoint list & is then summarised using LINQ
The simplified version of a custom object definition is shown below( & which is defined in the models area of an MVC application)
public class MyCustomObjectList
{
public string eventdate { get; set; }
public string userid { get; set; }
public string action { get; set; }
}
The JSON object is serialised into a MyCustomObjectList array.
var customobject = serializer.Deserialize<MyCustomObjectList>(jsonobject);
I wanted to work out how many actions of each type happened on a given day. NB eventdate is stored as a string in format yyyy-mm-dd hh:MM:ss. This was to simplify conversions between c#, JSON & Jquery ( where required I create DateTime objects elsewhere in the code using the
eventdate.
Some will argue this is inefficient, but I prefer to split processes into a sequential set of really simple operations, for the sake of easier debugging & to help other people follow my code. Thats why there are 2 Linq queries .
querya strips out the time component from the eventdate This ensures our later grouping happens by day, & not by second. To be doubly sure that there is no caching, I create it in a new field called actionday. I also rename action to activity, because intellisense was getting confused!! The other columns are copied as is.
var querya =
from c in customobject.rows
select new { actionday = c.eventdate.Substring(0, 10), activity = c.action, c.userid,
c.eventdate };
/* queryb produces a grouped count of querya, grouped on actionday & activity, creating new columns actionkey,ActionCount,Dte,action & DetailList ( which is a summary for debugging purposes)
*/
var queryb=
from p in querya group p by new { p.actionday, p.activity} into idGroup
actionkey = idGroup.Key,
ActionCount = idGroup.Count(),
Dte = idGroup.Key.actionday,
action = idGroup.Key.activity,
DetailList = idGroup
};
Here’s a version that sumarises by 3 columns
var queryc = from p in querya
group p by new { p.actionday, p.userid, p.activity} into idGroup
select new
{
actionday = idGroup.Key,
ActionCount = idGroup.Count(),
userid = idGroup.Key.userid,
Dte = idGroup.Key.actionday,
action = idGroup.Key.activity,
DetailList = idGroup
};